A problem with many water supply systems is the presence of micro-organisms in the system. These organisms may accumulate and reproduce at sites where the water stands still, for example at shower heads, faucets, sprinklers and so on. Static water in pipes at hospitals, military camps, sports centres, office complexes etc may cause growth and spread of harmful bacteria, for example Legionella bacteria. These, and other bacteria, may multiply under static conditions and at temperatures approximately between 20-50° C. Temperatures over 55° C. have been found to reduce or even eliminate bacterial growth.
The prior art suggests many ways of limiting the spread of bacteria or eliminating the existence of bacteria. WO 05/124236 describes a filter and radiation system. By placing the filter prior to the radiation step most of the bacteria, or other organisms, are captured and therefore only radiation sources of relatively low intensity are needed to deactivate the micro-organisms. Document '236 also describes that the radiation may be altered to adapt to the exposure time. For example, a higher intensity is needed for deactivating the running water coming from the filter compared to the static water around the tapping point (e.g. shower head, faucet, sprinkler). The drawbacks of '236 are the need of a radiation source and that the filter will either become clogged after a while and thereby becomes dysfunctional, or needs to be disposable. The latter is impractical, usually cost ineffective, not environmentally friendly, and there is a risk of dislodging the captured bacteria.
US-06/0151622 describes a solution to the problem by presenting a system where there is a constant water flow in the pipes, thereby avoiding static points. Additionally, the circulating water is maintained outside the critical temperature zone for bacteria multiplication of 20-50° C. Document '622 describes a system where hot water and cold water inlet pipes are connected to a return water pipe via a thermostat. The thermostat is set at an appropriate temperature, above or below a critical temperature, to control the temperature of the return water flow. Additionally, water flow adjustment valves may be placed prior to the thermostat for controlling the flow in the water return pipe.
Obviously there is a need for systems that can provide a constant flow and that can maintain a critical water temperature to reduce the risk of spreading of Legionella and other bacteria. The system should also be uncomplicated with minimum extra piping. The present invention provides such a system and is also applicable to many conventional water supply systems.